Apparatus and method for particle sampling during semiconductor device manufacturing

ABSTRACT

An apparatus for sampling particles from a processing chamber used in the fabrication of semiconductor devices includes a sampling line sequentially having a sampling port, a sampling air valve, a particle sampler and an isolation valve. A pumping line is connected between the isolation valve and a pump, and a discharge line is connected between the pump and a discharge port. The apparatus includes a purge line sequentially having a purge gas source, a purge air valve, and a divergence end. A purge-sampler line connects the divergence end to the sampling line between the sampling air valve and the particle sampler, and includes a purge-sampler air valve. A purge-pump line connects the divergence end to the pumping line, and includes a purge-pump air valve. The apparatus also includes an isolation valve bypass line connected at one end to the sampling line between the particle sampler and the isolation valve, connected at the other end to the pumping line between the isolation valve and the purge-pump line, and including a bypass air valve. A control unit controls the operation of the isolation valve, the pump, and the air valves.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a particle sampling apparatus and itsoperating method for semiconductor device manufacturing. Moreparticularly, the present invention relates to a particle samplingapparatus for sampling particles directly from the processing chamber ofa vacuum processor and its operating method.

2. Description of the Related Art

Semiconductor device manufacturing processes require very cleanprocessing environments. Several manufacturing processes, including LowPressure Chemical Vapor Deposition (LPCVD), Plasma Enhanced ChemicalVapor Deposition (PECVD), dry etch, sputtering, and ion injection,require a vacuum state during processing. The above processes aresubject to various failures depending on the processing equipment andthe corresponding processing gas used. A great number of failures ofsemiconductor devices are caused by particles generated in a processingchamber. In order to determine how to minimize and contain thesedamaging particles, it is necessary to analyze and quantify thedistribution of generated particles.

Conventionally, the particles and defects present on wafers are analyzedafter the wafers are processed and removed from the chamber. However, itis often impossible to determine the exact cause of the damagingparticles because the particles can not be observed during the sequenceof events carried out in the chamber during a process.

An impactor is one conventional device that is capable of directlysampling particles from a processing chamber. However, a drawback of theimpactor is that it is designed to sample such particles only while ahigh pressure process is being performed in the process chamber.

Referring to FIG. 1, an impactor or particle sampler 10, collectsparticles by passing a gas released directly from inside the processingchamber through the sampler from the left inlet to the right outlet asdesignated by the arrows in FIG. 1. Particle collection wafers areplaced on stages 14 and 15 oriented perpendicular to the direction ofgas flow. For example, the particle sampler 10 in FIG. 1 has two stages,a first stage 14 and a second stage 15. A first nozzle 12 and a secondnozzle 13 are formed facing stages 14 and 15, respectively; and nozzles12 and 13 have different diameters.

When a pressure gradient is applied from the left inlet to the rightoutlet of the particle sampler 10, sample air containing particlespasses through the first nozzle 12, and collides with the collectingwafer on the first stage 14 by inertia so that the particles arecollected according to the speed and the mass of the particles. Then,the sample gas that collided with the first stage 14 passes through thesecond nozzle 13 having a smaller diameter than that of the first nozzle12 so that the gas and particles are accelerated. The acceleratedparticles collide with the collecting wafer on the second stage 15. Whenthe speed of the sample gas is sufficiently fast, very small particleswill collide with, and can be collected on, the collecting wafer.

Conventionally, the impactor particle sampler is used for the collectionof particles when the processing chamber is under high pressure.However, it cannot be used if the sampled gas is poisonous. If theprocessing gas in the processing chamber is poisonous, it must bereplaced with a safer gas, such as nitrogen gas, before particlesampling is performed.

During vacuum processing, on the other hand, particle sampling can onlybe carried out using a vacuum pump to establish a pressure differencebetween the processing chamber and a pumping line downstream of theparticle sampler. Particle sampling is accomplished using equipment witha sampling port that can be connected to the processing chamber, and acut-off valve, a particle sampler, and another cut-off valve, installedin sequential order on a line from the sampling port. The sample gas isdischarged through a discharge line by the vacuum pump. Then, while avacuum process is performed in the processing chamber, the cut-offvalves are opened for a certain time and some contents from theprocessing chamber are passed through the particle sampler where theparticles are collected. The cut-off valves are then closed; then theparticle sampler is disconnected from the processing chamber. Next, thecollecting wafers are dismounted from the stages and particles on thecollecting wafers are then analyzed.

If a vacuum process in the processing chamber is performed at a highenough vacuum, i.e., a low enough pressure, the vacuum pump of theparticle collecting system can not maintain the proper pressuregradient. Then gas in the particle sampler may move in the oppositedirection, carrying particles into the processing chamber. Thiscondition is called back-flow, and it is undesirable because itincreases the likelihood of damage to the semiconductor device in theprocessing chamber.

In addition, the particle sampler containing the collected particlesmust be completely purged before it is ready for subsequent use. Afterpurging, the particle sampler must be reconnected to the processingchamber. However, the reconnecting task can again contaminate theparticle sampler so that extra particles are introduced into thesampler. This can lead to a failure of the particle sampler to providean accurate sample for analysis.

Thus there is a need for a particle sampling apparatus that can directlysample particles from a process chamber reliably, repeatedly andefficiently, whether the chamber is in a high pressure state or anextremely low pressure state. At high pressure, leaks must be prevented.At low pressure back-flow must be prevented. Purging must be leak proofand should not require disconnecting and reconnecting the apparatus tothe chamber, to prevent contamination of the sampler after purging.

SUMMARY OF THE INVENTION

The present invention is directed to a particle sampling apparatus andits operating method having an internal purge system to provide reliableparticle analysis. The present invention is further directed tomaintaining a proper pressure difference between a high vacuumprocessing chamber and a pumping line. The present invention is alsodirected to preventing back-flow of sample gas into the processingchamber. The present invention is also directed to a particle samplingmethod that can be manual or automated.

To achieve these and other objects and advantages of the presentinvention a sampling apparatus for particle analysis comprises asampling line including, in order, a sampling port, a sampling airvalve, a particle sampler and an isolation valve, a pumping lineconnected between the isolation valve and a pump, and a discharge lineconnected between the pump and a discharge port. The apparatus includesa purge line having, in order, a purge gas source, a purge air valve,and a divergence end. A purge-sampler line connects the divergence endto the sampling line between the sampling air valve and the particlesampler, and includes a purge-sampler air valve. A purge-pump lineconnects the divergence end to the pumping line, and includes apurge-pump air valve. The apparatus also includes an isolation valvebypass line connected at one end to the sampling line between theparticle sampler and the isolation valve, connected at the other end tothe pumping line between the isolation valve and the purge-pump line,and including a bypass air valve. A control unit controls the operationof the isolation valve, the pump, and the above named air valves.

Another aspect of the present invention is a method for samplingparticles from a processing chamber used in the fabrication ofsemiconductor devices. The method includes establishing a predetermineddriving pressure inside a pumping line at a pressure level lower than apredetermined process pressure of a process gas inside a processingchamber. The next step is prepurging a particle sampler on a samplingline connected between the processing chamber and the pumping line witha purge gas by establishing flow communication both between a purge gassource on a purge line and the particle sampler and also between theparticle sampler and the pumping line. The next step is reducingpressure inside the particle sampler to a level below the processpressure by terminating flow communication between the purge gas sourceand the particle sampler. Then the method calls for sampling the processgas for a predetermined sampling time by establishing flow communicationbetween the processing chamber and the particle sampler. The final stepis postpurging the particle sampler with the purge gas by terminatingflow communication between the processing chamber and the particlesampler and establishing flow communication between the purge gas sourceand the particle sampler.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail with reference to the accompanyingdrawings in which:

FIG. 1 is a sectional view of a prior art impactor or particlecollector;

FIG. 2 is a schematic configuration of the particle sampling apparatusaccording to one embodiment of the present invention;

FIG. 3 is a detailed representation of an embodiment of the presentparticle sampling apparatus installed on a cart;

FIG. 4 is a schematic representation of the particle sampling apparatusaccording to an embodiment of the present invention employed with asemiconductor device manufacturing system;

FIG. 5 is a flow chart illustrating a method for operating the particlesampling apparatus of the present invention during the preparation(establishing) step according to an embodiment of the present methodinvention;

FIG. 6 is a flow chart illustrating a method for operating the particlesampling apparatus of the present invention during the prepurge stepaccording to an embodiment of the present method invention;

FIG. 7 is a flow chart illustrating a method for operating the particlesampling apparatus of the present invention during the pumping(reducing) step according to an embodiment of the present methodinvention;

FIG. 8 is a flow chart illustrating a method for operating the particlesampling apparatus of the present invention during the sampling stepaccording to an embodiment of the present method invention; and

FIG. 9 is a flow chart illustrating a method for operating the particlesampling apparatus of the present invention during the postpurging stepaccording to an embodiment of the present method invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 is a schematic configuration of the particle sampling apparatusaccording to a preferred embodiment of the present invention and is usedto describe the apparatus of the present invention.

The particle sampling apparatus of the present invention includes asampling line 60, a pumping line 62, a discharge line 64, a purge line66, a purge-pump line 65, a purge-sampler line 67, a bypass line 68, anda control unit (56 in FIG. 3). The basic flow path for gas duringparticle sampling starts at the sampling port 24 (which can be connectedto a processing chamber), passes via the sampling line 60 through aparticle sampler 10 and into an isolation valve 22, passes via thepumping line 62 into a pumping device 20, and passes via the dischargeline 64 into a discharge port 28.

The components of the sampling line 60 are first described. The samplingport 24 is for connection to a specific location on the processingchamber. In the processing chamber various vacuum process, such asLPCVD, PECVD, dry etching, ion injection or sputtering, can beperformed.

A sampling air valve 34d is connected on the sampling line between thesampling port 24 and the particle sampler 10. This valve is used tocontrol the flow of process gas from the processing chamber (not shown)to the particle sampler 10. In FIG. 2 the inlet of the particle sampleris at the right and the outlet is at the left, which is reversed fromFIG. 1.

Recall that in FIG. 1 the conventional particle sampler 10 collectedparticles by passing gas from the inside of the processing chamberthrough the particle sampler. Particles are collected on wafers, forexample small wafers having a size of 1 centimeter (cm) by 1 cm, placedon one or more stages 14, such as the first stage 14 and the secondstage 15 in FIG. 1. Each stage 14 is oriented so that its planar area isperpendicular the direction of gas flow. A nozzle 12 faces each stage14, for example the first nozzle 12 and the second nozzle 13 of FIG. 1are installed on the front side of the respective stage 14 and 15. Inthe preferred embodiment the particle sampler 10 has a third stage (seeFIG. 4) having a different diameter.

After sampling is completed the particle sampler 10 is disconnected fromthe particle sampling apparatus of the present invention, removed tosome conventional analysis equipment, and is disassembled so that thewafers with the collected particles can be extracted. The collectedparticles on the wafers are then analyzed for their elements, size, anddistribution, for example, by SEM (Scanning Electron Microscope) or AES(Auger Electron Spectroscopy) equipment. After the particle analysis iscompleted, the particle sampler 10 is again assembled with newcollection wafers, and is reconnected to the particle sampling apparatusof the present invention so as to be ready to perform a new samplingprocess.

Referring to FIG. 2, a suitable particle sampler 10 includes theabove-described two and three stage impactors, as well as an apparatuswith multiple impactors arranged in parallel (dotted lines in FIG. 2). Aset of parallel impactors allow the particle sampling process to beperformed sequentially even when one impactor is disconnected for aseparate analysis, or when particle sampling is to be separatelyperformed at different times during a single process inside theprocessing chamber. Such sequential sampling is controlled by additionalvalves connected to the other particle samplers though any conventionalmeans.

In the preferred embodiment, the particle sampler 10 is installedhorizontally to maintain a constant flow of processing gas, with theinlet toward the sampling port 24. Leakage of sampling gas is preventedby installing a support ring (not shown) on each stage.

An isolation valve 22 is also connected on the sampling line 60 at theend opposite to the sampling port 24. In the preferred embodiment, theisolation valve 22 is a cut-off valve which performs only an on/offfunction. In other embodiments of the present invention, a valve thatmore gradually controls the amount of the gas flow can be used as theisolation valve 22. In the preferred embodiment, a manual valve 39 isalso connected on the sampling line 60 between the sampling air valve34d and the particle sampler 10.

The elements of the pumping line 62 are described next. The pumping line62 includes a pumping device 20. In the preferred embodiment, thesampling line pumping device 20 includes a rotary pump and a turbo pumpconnected in series at the front end of the rotary pump. This preferredcombination enables the efficient sampling of particles even during highvacuum processes in the processing chamber. Alternatively, the pumpingdevice 20 may comprise only a rotary pump.

In some embodiments of the apparatus of the present invention, pressuresensors 30 and pressure switches 32 are included. A pressure sensormeasures multiple pressure values in a range, while a pressure switch isin an "on" state up to a specific pressure and is in an "off" state athigher pressures. In the preferred embodiment the pressure sensors 30are capacitance manometers (CM).

In the preferred embodiment, a pumping capacitance manometer (CM1) 30aand a pumping pressure switch 32a are installed on the pump line 62between the isolation valve 22 and the pumping device 20. The CM1 30ameasures a pressure value in a range from about 0 Torr (millimeters ofmercury at 0° C.) to 1 Torr. The pumping pressure switch 32a is operatedup to a predetermined pressure value, for example 75 Torr.

A discharge line 64 connects the pumping device 20 to the discharge port28. No additional elements are connected to the discharge line 64.

Next are described elements on the three purge related lines, the mainpurge line 66, the purge-pump line 65, and the purge-sampler line 67.The purpose of the purge related lines is to clear the particle sampler10 before and after the sampling phase of the operation using a purgegas, for example nitrogen gas.

The main purge line 66 starts from a purge gas source 26b and divides ata divergence point into a plurality of other purge related lines. Apurge-sampler line 67 is connected from the divergence point to ajuncture on the sampling line 60 between the particle sampler 10 and thesampling valve 34d. In the preferred embodiment, the juncture is betweenthe particle sampler 10 and the manual valve 39. A purge-pump line 65 isconnected from the divergence point to a juncture on the pumping line 62between the isolation valve 22 and the pumping device 20. In thepreferred embodiment, this juncture is between the isolation valve 22and the pumping capacitance manometer (CM1) 30a. A purge air valve (AV2)34b is connected on the main purge line 66, a purge-sampler air valve(AV3) 34c is connected on the purge-sampler line 67, and a purge-pumpair valve (AV1) 34a is connected on the purge-pump line 65.

In the preferred embodiment, additional elements are connected on thepurge related lines as follows. A purge pressure switch (PS3) 32c, apurge regulator 38a, and the purge air valve (AV2) 34b are connected onthe main purge line 66, in order, from the purge gas source 26b. Apurge-sampler needle valve 36b, the purge-sampler air valve (AV3) 34c, apurge-sampler pressure switch (PS2) 32b, and a purge-sampler capacitancemanometer (CM3) 30c are connected on the purge-sampler line 67, inorder, from the divergence point. A filter F may be installed betweenthe purge-sampler pressure switch 32b and the purge-sampler capacitancemanometer (CM3) 30c. In order, from the divergence point on thepurge-pump line 65, a purge-pump needle valve 36a and the purge-pump airvalve (AV1) 34a are connected. The needle valves 36 control the rate offlow of the purge gas through the purge-pump line 65 and thepurge-sampler line 67. A control line 70 is connected with the purgeline 66 and is used for controlling the air valves 34. The control lineoriginates from an air supply source 26a, passes through an airregulator 38b and connects with the main purge line 66 between the purgegas source 26b and the purge pressure switch 32c.

Finally, the isolation valve bypass line 68 is described. The bypassline 68 bypasses the isolation valve 22, and connects the sampling line60 at a point between the particle sampler 10 and the isolation valve 22to the pumping line 62 at a juncture between the isolation valve 22 andthe purge-pump line 65. The bypass line 68 includes a bypass air valve(AV5) 34e. In the preferred embodiment, the bypass line 68 hasconnected, in order from the sampling line 60, a bypass capacitancemanometer (CM2) 30b and the bypass air valve (AV5) 34e.

The pumping device 20, isolation valve 22, and air valves 34 can becontrolled manually or automatically. In the preferred embodiment, everyelement of the particle sampling apparatus, including, for example, eachair valve 34, isolation valve 22, and pumping device 20, isautomatically controlled by a control unit (56 in FIG. 3).

FIG. 3 is a detailed representation of one embodiment of the presentparticle sampling apparatus including a cart. The elements of theparticle sampling apparatus of FIG. 2 are contained inside a frame 50,having for example a hexahedron-shape, and a plurality of rollers 52fixed under the frame 50 to enable movement. In addition, the particlesampling apparatus can be fixed in position by extending a plurality ofsupports 54. A knob 58 is formed on the upper side of the frame 50. Theparticle sampler 10 is mounted horizontally on the top side of the frame50, the pumping device 20 is mounted on the bottom of the frame 50, theisolation valve 22 is mounted vertically inside the frame 50, and thepumping line 62, the purge line 66, the purge-pump line 65, and thepurge-sampler line 67 are all within the frame 50. A control unit 56,such as an LED-touch screen, is formed on the top side of the framedisposed toward knob 58. In the control unit 56, all actuators such asvalves are controlled manually or automatically. The purge gas source26b and the discharge port 28 pass through a side of the frame 50.

FIG. 4 is a schematic representation of the particle sampling apparatusaccording to an embodiment of the present invention employed with asemiconductor device manufacturing system. Sampling port 24 is coupledat one end to a processing chamber 40. Sampling gas is pumped through aparticle sampler 10, a pumping device 20, and a discharge port 28. Purgegas is supplied from a purge gas supply source 26b to the samplingapparatus. A throttle valve 42, a turbo pump 44, and a rotary pump 46are installed in order from the lower end of the processing chamber 40to maintain the processing chamber 40 in a vacuum state. The pumpingdevice 20 may comprise a turbo pump and a rotary pump to balance thevacuum pressures of the sampling apparatus with those of the processingchamber.

In the preferred embodiment, the actuators of the pumping device 20, theisolation valve 22, and the various air valves 34 are interlocked toprovide stable processing and to prevent damage. Referring to FIG. 2,the interlocking relationships are described specifically in thefollowing. The pumping device 20 is interlocked with the isolation valve22 such that the pumping device 20 is "on", i.e., the pumping device 20is running, when the isolation valve 22 is open. Likewise, the pumpingdevice 20 is interlocked to an "on" position when either the samplingair valve 34d or the bypass air valve 34e is open. The isolation valve22 is not closed when the sampling air valve 34d is open or when thepurge and the purge-sampler air valves 34b and 34c are open, and theisolation valve 22 is interlocked to a closed position when the pumpingdevice 20 is off. The purge-pump air valve 34a is interlocked to aclosed position when the isolation valve 22 is open, or when the bypassair valve 34e or the purge-sampler air valve 34c is open. The purge airvalve 34b is interlocked to a closed position when the sampling airvalve 34d is open. The purge-sampler air valve 34c is interlocked to aclosed position when the purge-pump air valve 34a is open. The samplingair valve 34d is interlocked to a closed position when the purge-pump,the purge, and the purge-sampler air valves 34a, 34b, and 34c are open;when the isolation valve 22 is closed; or when the pumping device 20 is"on" with the pressure of the bypass capacitance manometer (CM2) 30bhigher than the process pressure and the purge-sampler pressure switch32b "on". The bypass air valve 34e is interlocked to a closed positionwhen the purge and purge-sampler air valves 34b and 34c are open, andthe pumping device 20 is operating.

The operating method of the present invention includes preparation forestablishing a driving pressure, prepurge for clearing out the particlesampler with a purge gas, pumping for reducing the pressure in theparticle sampler, sampling for passing the process gas from theprocessing chamber into the particle sampler, and postpurge for clearingthe process gas out of the particle sampler. After these steps theparticle sampling method is complete. Referring to FIG. 5 through FIG. 9and to FIG. 2, the preferred embodiment of the operating methodaccording to the present invention is illustrated in detail.

FIG. 5 illustrates the preferred embodiment of the preparation step inwhich a driving pressure is established in the pumping line. First thepurge-pump air valve (AV1) 34a and the purge air valve (AV2) 34b areclosed, and the pumping device 20 is turned "on". If a pump-linepressure measured by the purge-pump pressure sensor (CM1) 30a, forexample a capacitance manometer, falls to a predetermined drivingpressure, for example 500 milliTorr (mTorr), then an adequate vacuumexists to continue processing and the bypass air valve 34e is opened. Apumping period of time is measured from the start of the pumping using atimer within the control unit. If the pump-line pressure does not fallto the driving pressure, for example 500 mTorr, while the pumping periodis less than or equal to a predetermined maximum pumping time, forexample 60 seconds, a leak in the pumping line 62 is indicated and soprocessing does not continue. In this case the method ceases and thepurge-pump air valve (AV1) 34a and the purge air valve (AV2) 34b areopened.

When the pump-line pressure measured by CM1 30b is at or below thedriving pressure, the bypass air valve (AV5) 34e is opened and the partof the sampling line 60 including the particle sampler 10 is evacuatedby pumping through the bypass line 68. If a bypass pressure measured bythe bypass pressure sensor (CM2) 30b, for example a capacitancemanometer, also falls to the driving pressure, for example 500 mTorr,the preparation step is complete and the prepurge step begins. A bypasspumping period of time is measured from the start of the bypass pumpingusing the timer. If the bypass pressure does not fall to the drivingpressure, for example 500 mTorr, while the bypass pumping period is lessthan or equal to the predetermined maximum pumping time, for example 60seconds, a leak in the sampling line 62 is indicated and so processingdoes not continue. In this case the method ceases and the purge-pump airvalve (AV1) 34a and the purge air valve (AV2) 34b are opened.

FIG. 6 is a flow chart illustrating the preferred embodiment of thepresent method during the prepurge step, i.e., from the start of theprepurge step to the start of the pumping (reducing) step. The prepurgestep is carried out by closing the bypass air valve (AV5) 34e, openingthe isolation valve (IV) 22, and opening the purge air valve (AV2) 34band the purge-sampler air valve (AV3) 34c. These operations allow apurge gas, such as nitrogen gas substantially free of particles, to flowfrom the purge gas source 26b into the particle sampler 10 and clear itout. The prepurge step continues until a prepurge period, begun when theabove air valves are opened, reaches a predetermined prepurge time. Atthat time prepurge is complete. Thereafter the pumping (reducing)process follows.

FIG. 7 is a flow chart illustrating the preferred embodiment of thepresent method during the pumping (reducing) step, i.e., from thebeginning of the pumping (reducing) step to the beginning of thesampling step. After normal completion of prepurge and pumping(reducing), the sampling starts. The pumping (reducing) step starts byclosing the purge-sampler air valve (AV3) 34c and the purge air valve(AV2) 34b. Successful sampling requires that the pressure at the outletof the particle sampler, measured as a reducing pressure by the bypasspressure sensor (CM2) 30b, for example a capacitance manometer, is belowthe predetermined process pressure (also called a "standard pressure")inside the processing chamber. The purpose of the reducing step is toachieve this process pressure at the bypass pressure sensor (CM2) 30b bypumping with the pumping device 20. When the reducing pressure measuredby the bypass pressure sensor (CM2) 30b falls to the process pressure orbelow, reducing is complete and sampling begins. However, a timer isinitiated to measure a reducing period from the time of the opening ofair valves 34c and 34b. When the pressure fails to fall below theprocess pressure by the time the reducing period exceeds a predeterminedmaximum reduction time, for example 180 seconds, the failure isindicative of a leak in the pumping line or sampling line, so processingdoes not continue. In this case the method ceases; the isolation valve22 is closed, and the purge-pump air valve (AV1) 34a and the purge airvalve (AV2) 34b are opened.

FIG. 8 is a flow chart illustrating the preferred embodiment of thepresent method during the sampling step, i.e., from the beginning of thesampling step to the beginning of the postpurging step. The samplingprocess begins when the sampling air valve (AV4) 34d is opened whichallows process gas to enter the particle sampler 10, driven by thedifference in the process pressure of the processing chamber and thereducing pressure. A timer is initiated to measure a sampling periodwhen the sampling valve is opened. When the sampling period exceeds apredetermined sampling time set up by the processing recipe, thesampling is completed normally. However, the sampling is stopped beforethe sampling period exceeds the predetermined sampling time if any backflow is detected. In the preferred embodiment checking the back flow isoptional. If back flow is checked, it is done using the purge-samplerpressure sensor (CM3) 30c to monitor a back pressure. A back stream rateis set up in the processing recipe. The back stream rate is a pressuredetermined in relation to the process pressure and a rate established bythe processing recipe (process pressure--process pressure/rate). If theback pressure ever equals or exceeds the back stream rate during thesampling time, conditions favor back flow and there is danger that gaswill flow from the particle sampler back to the process chamber.Therefore, if back flow is checked and the back pressure equals orexceeds the back stream rate during the sampling time, the sampling stepis treated as complete.

FIG. 9 is a flow chart illustrating the preferred embodiment of thepresent method during the postpurge step, i.e., from the beginning ofthe postpurge step to the completion of processing. The sampling airvalve (AV4) 34d is closed to stop the flow of process gas and terminatesampling and a timer is initiated to measure a stand-by period. Then,when the stand-by period exceeds a predetermined stand-by time, forexample 1 second, the purge air valve 34b and the purge-sampler airvalve 34c are opened to allow purge gas to enter the sampling line andthe particle sampler. The stand-by time serves to prevent the occurrenceof a back stream of purge gas into the processing chamber.

A timer is initiated to measure a postpurge period beginning upon theopening of the purge air valve 34b and the purge-sampler air valve 34c.In this state, purge gas is driven through the particle sampler 10 bythe pumping device 20. When the postpurge period exceeds a predeterminedpostpurge time as set up in the processing recipe, the isolation valve22 is closed. This terminates the pumping of the purge gas through theparticle sampler 10 and should lead to the build up of purge gas andpurge gas pressure in the sampling line. This is desirable to eliminatethe vacuum in the sampling line 60 and bring both the sampling line 60and the particle sampler 10 up to target pressure near the ambient roompressure before disconnecting the particle sampler 10. To ensurepressure in the sampling line 60 and particle sampler 10 reach thetarget pressure, either the purge-sampler pressure switch (PS2) 32b mustdetect a pressure above the target pressure and close the purge-samplerneedle valve (NV2) 36b, or the postpurge step must pause a predeterminedswitch time, for example 10 seconds, after closing the isolation valve22. A timer is initiated to measure a switching period when theisolation valve 22 is closed.

If the switching period equals or exceeds the predetermined switchingtime, then the purge-sampler pressure switch (PS2) 32b turns off, or thepurge-sampler needle valve (NV2) 36b opens. Then the purge-sampler airvalve 34c closes, the purge-pump air valve 34a opens, and the process iscomplete at the predetermined switching time.

If the second pressure switch (PS2) 32b is on while the switching periodis less than the predetermined switching time, the purge-sampler airvalve 34c is closed, and the purge-pump air valve 34a is open, andprocessing is complete at this time, earlier than the predeterminedswitching time.

After completion of the particle sampling the processing is complete andthe particle sampler 10 is disconnected from the apparatus, removed, anddisassembled for particle analysis.

Accordingly, the present invention including an internal purge systemprovides for improved particle analysis. In addition, the presentinvention including an internal pump, allows the particle sampling to becarried out even during vacuum processing conditions inside theprocessing chamber thereby providing accurate particle analysis for abroader range of semiconductor device fabrication processes. Further,since the back stream of sampling gas into the processing chamber isprevented during sampling, particle sampling is carried out withoutincreasing the likelihood of malfunctions in the processing chamberwhich adversely affect the semiconductor devices.

While preferred embodiments of the present invention have beendescribed, it will be understood by those skilled in the art thatvarious changes and modifications may be made, and equivalents may besubstituted for elements thereof, without departing from the true scopeand spirit of the present invention. Therefore, it is intended that thepresent invention not be limited to the particular embodimentsdisclosed, but that the present invention include all embodimentsfalling within the scope of the appended claims and their equivalents.

What is claimed is:
 1. An apparatus for sampling particles, comprising:asampling line sequentially including a sampling port, a sampling airvalve, a particle sampler and an isolation valve; a pumping lineconnected between the isolation valve and a pump; a discharge lineconnected between the pump and a discharge port; a purge linesequentially including a purge gas source, a purge air valve, and adivergence end; a purge-sampler line connecting the divergence end tothe sampling line between the sampling air valve and the particlesampler, and including a purge-sampler air valve; a purge-pump lineconnecting the divergence end to the pumping line, and including apurge-pump air valve; an isolation valve bypass line connected at oneend to the sampling line between the particle sampler and the isolationvalve, connected at the other end to the pumping line between theisolation valve and the purge-pump line, and including a bypass airvalve; and a control unit for controlling the operation of the isolationvalve, the pump, the sampling air valve, the purge air valve, thepurge-sampler air valve, the purge-pump air valve, and the bypass airvalve.
 2. The apparatus of claim 1, further comprising a manual valveconnected on the sampling line between the sampling air valve and thepurge-sampler line.
 3. The apparatus of claim 1, further comprising apurge regulator connected on the purge line between the purge gas sourceand the purge air valve.
 4. The apparatus of claim 1, furthercomprising:a purge-pump needle valve connected on the purge-pump linebetween the divergence end and the purge-pump air valve, and apurge-sampler needle valve connected on the purge-sampler line betweenthe divergence end and the purge-sampler air valve.
 5. The apparatus ofclaim 1, further comprising an additional particle sampler connected onthe sampling line in parallel with the particle sampler.
 6. Theapparatus of claim 1, the particle sampler comprising three stagesoriented to be perpendicular to a horizontal flow of a sample gas. 7.The apparatus of claim 1, further comprising a filter inside thepurgesampler line.
 8. The apparatus of claim 1, further comprising:apumping pressure switch connected on the pumping line; a purge-samplerpressure switch connected on the purge-sampler line between thepurge-sampler air valve and the sampling line; and a purge pressureswitch connected on the purge line between the purge gas source and thepurge air valve.
 9. The apparatus of claim 1, further comprising amovable cart for holding the sampling line, the pumping line, thedischarge line, the purge line, the purge-sampler line, the purge-pumpline, the bypass line, and the control unit.
 10. The apparatus of claim1, further comprising:a pumping pressure sensor connected on the pumpingline; a bypass pressure sensor connected on the bypass line between thesampling line and the bypass air valve; and a purge-sampler pressuresensor connected on the purge-sampler line between the sampling line andthe purge-sampler air valve.
 11. The apparatus of claim 10, wherein thepumping pressure sensor, the bypass pressure sensor, and thepurge-sampler pressure sensor are capacitance manometers.
 12. Theapparatus of claim 11, the pump further comprising a turbo pumpconnected between the pumping line and the rotary pump.
 13. Theapparatus of claim 12, further comprising a chamber vacuum pumpconnected to the vacuum chamber for maintaining a process gas inside thevacuum chamber at a predetermined process pressure.
 14. The apparatus ofclaim 1, wherein the pump comprises a rotary pump.
 15. The apparatus ofclaim 1, further comprising a vacuum chamber connected to the samplingport for the fabrication of a semiconductor device.